It is known that more lithium ions per unit volume can be intercalated into silicon materials, such as silicon (Si) and silicon oxides represented by SiOx, than into carbon materials, such as graphite. In particular, the volume change due to the intercalation, of lithium ions is smaller in SiOx than in Si, and application of SiOx to a negative electrode of lithium-ion batteries has been investigated. For example, Patent Literature 1 discloses a non-aqueous electrolyte secondary battery that contains a mixture of SiOx and graphite as a negative-electrode active material.
However, non-aqueous electrolyte secondary batteries that contain SiOx as a negative-electrode active, material have lower initial charge/discharge efficiency than non-aqueous electrolyte secondary batteries that contain graphite as a negative-electrode active material. This is mainly because an electrochemical reaction during charging produces an irreversible compound, such as Li4SiO4, and produces irreversible capacity. Patent Literature 2 proposes a negative-electrode active material represented by SiLixOy (0<x<1.0, 0<y<1.5) containing a Li silicate in order to reduce such irreversible capacity. Patent Literature 3 proposes a negative electrode material containing a combination of a Si/SiO2/Li4SiO4 three-phase composite structure oxide and carbon.